Aquahot 431/12 Keeps Tripping Hi-Limit Thermostats

[Croom352]

We have a Aquahot 431/12. Burner wouldn't fire. Performed pinpoint test and found both hi-temp thermostats open circuit. Replaced them only to have the same thing happen again.

I have now replaced all the thermostats, started boiling, shutoff but too late. Both high limits went bad again.

 

Did a component test on the controller which passed. Then I did ohm test on the C- plug on the controller side. C-1 and C-5 have continuity. Don't believe that is right.

 

Plus add off the market controller. Spheres SG 1553/ 12v.

 

Do I need Controller WPE-300-901?  Or further testing?

I don't want to just keep throwing parts at it, but rather get to the root cause of this problem.

Thanks!

 

[timaz996]

Are you saying both diesel and electric high temp thermostats?  

[Tom Cherry]

1 hour ago, Croom352 said:

We have a Aquahot 431/12. Burner wouldn't fire. Performed pinpoint test and found both hi-temp thermostats open circuit. Replaced them only to have the same thing happen again.

I have now replaced all the thermostats, started boiling, shutoff but too late. Both high limits went bad again.

 

 

 

Did a component test on the controller which passed. Then I did ohm test on the C- plug on the controller side. C-1 and C-5 have continuity. Don't believe that is right.

 

 

 

Plus add off the market controller. Spheres SG 1553/ 12v.

 

 

 

Do I need Controller WPE-300-901?  Or further testing?

 

I don't want to just keep throwing parts at it, but rather get to the root cause of this problem.

Thanks!

 

 

Have you called AH tech support.  They are informative and knowledgeable 

[Croom352]

Yes, both hi-limit trip when on diesel. We're running on electric only now with a new AC high limit thermostat. Seems to be only diesel that is causing the issue. Believe the issue is the DC control thermostat circuit in the controller might not be working or shorted causing the burner to stay running until the hi-limit trips and shuts off fuel solenoid.

[radioman]

22 hours ago, Croom352 said:

Yes, both hi-limit trip when on diesel. We're running on electric only now with a new AC high limit thermostat. Seems to be only diesel that is causing the issue. Believe the issue is the DC control thermostat circuit in the controller might not be working or shorted causing the burner to stay running until the hi-limit trips and shuts off fuel solenoid.

There is not a thermostat inside the control Box. The control box sends 12 volt out the orange wire on the C Plug to your regular thermostat. If the regular thermostat is calling for heat around 160F the switch will close and send the 12 volt back to the burner control on the C plug white wire and that starts the cycle. What you need to do is unplug one of the wire going to the regular thermostat if your burner stops burning you have a bad regular thermostat if it keeps burning you have a bad controller 

[96 EVO]

JMO, I think Aqua Hot realized they had an issue with heat buildup in the cabinet, prematurely affecting the controller.

On later model 450-D models, they suggested you toss the rubber boot that sealed the combustion intake to the compartment floor. This allowed fresh air into the burner compartment.

Last time I serviced my burner, I didn't put the cover back on, which will allow any heat next to the controller to dissipate into the compartment the unit is in. The noise difference is minimal.

 

 

[Ivan K]

On 4/19/2023 at 2:38 PM, Croom352 said:

Did a component test on the controller which passed. Then I did ohm test on the C- plug on the controller side. C-1 and C-5 have continuity. Don't believe that is right.

Rick, I pulley spare controller and meassured between C1 and C5, like in the picture. 9 Mega Ohm one way and totally open the other, appears there would be a diode or transistor in that circuit. Wish someone came up with a diagram for that board.

 

BTW,  are you saying that the high temp thermostats are one time use only?

Edited April 21, 2023 by Ivan K

[Croom352]

Yes, the hi-limit thermostats are a one time trip and then you have to replace. There is no trip switch on them. It would be great if we could have a more detailed electrical schematic for the aquahot.

This morning I'm going to ohm test the VDC Control thermostat wiring to the controller to make sure they aren't shorted together causing it to stay on. If it tests ok, then order new controller.

Oh and thank you for UPS stores. We have been on the road and just have them FedEx to the one nearest us. John at Heatmyrv has shipped all of our parts right away.

[Croom352]

After checking the wiring, the issue was the short from C1 to C5 on the controller.

Replaced controller.

Normal operation.

Thanks for everyone's help.